Cutting instruments such as knives and scissors have found ubiquitous use in modern society. Keeping these utensils sharp has constituted a concomitant major problem following their use. The most fundamental implement for sharpening knives and scissors has taken the form of a sharpening stone. In its simplest form, the stone has a flat surface, which perhaps may form one side of a solid polygon. Ultimately, the stone may increase in sophistication into the apparatus known as a grinding wheel. This rotates a stone in the form of a solid disk about its central axis. The edge of this disk, generally having a flat configuration on planes passing through the disk's center, contacts the knife's or scissors' edge to reform it into a sharp cutting instrument.
Whatever the form the stone may assume, it has proven successful in removing adequate amounts of material from around the cutting edge of either a knife or scissors to accomplish this sharpening process. However, such stones prove difficult in use and display substantial accompanying short comes.
Thus, a flat stone rubbed manually across a knife's or scissors' edge requires substantial sophistication on the part of the user to achieve a smooth, straight edge. Otherwise, the stone may remove too much material from some part of the cutting instrument and not enough from other parts. Further, the sharpening generally should proceed in stages; otherwise, the edge of a knife, in particular, will tend to apparently bend in one direction or the other and suffer reduced effectiveness. Further, of course, the manual use of the stone exposes a person's fingers to the cutting edge with the undesirable consequences of severe lacerations.
All of the problems, with the possible exception of cutting one's fingers, become exacerbated with a rotating sharpening stone. In the classic type of rotating stone, the person effectuating the sharpening moves the knife or scissors across the edge of the stone. For all of the reasons discussed above, this requires substantial skill on part of the operator to achieve a smooth even cutting edge across the length of the knife or scissors. Furthermore, the sharpening must proceed in stages on either side of the knife until the last process refines and smoothes the edge produced by the prior stages. The final smoothing of both sides of the knife and scissors constitutes a process called "honing" which will remove burrs and minor irregularities produced by the earlier stages. All of this, again, requires substantial skill.
Recent developments in sharpening devices have attempted to overcome the problems seen with the prior devices discussed above. Thus, one electric knife sharpener attempts to place a knife at a predetermined angle against the side of a small rotating sharpening stone in the form of a disk. After completing the grinding on one side of the knife, the operator, usually an amateur, places the knife in a holder at the similar preset angle on the other side of the rotating disk to grind on the knife's second side. This type of device does simplify the process of achieving a correct angle at the knife edge. However, it does not achieve the uniform removal of material throughout the length of the knife. More importantly, it does not assist in the final or honing process. Furthermore, this type of grinding stone can easily remove far too much material from one side of the knife and almost preclude the successful achievement of a straight smooth line along the entire knife. Thus the use of the home electric sharpener still requires the use of substantial skill to achieve the desired edge. Furthermore, this type of sharpener has found very little, if any, use for improving the cutting edges of scissors.
Other knife sharpeners simply take two stones and place them together with an edge of each of the stones coming together to form a V. The V sits within some form of a holding device. The user then pulls the knife through the stones in the form of the V to simultaneously remove material from both sides of the knife's edge. While this type of device simplifies the sharpening process, it still does not adroitly guide the user through the final or honing stages of the process. In addition, pulling the knife through the V of this type of device may cause it to contact and mar the surface upon which the sharpener sits.
The development of sharpeners for scissors has taken a different tack. Current sharpeners typically include a plate having two openings into each of which one blade of the scissors passes. The openings have a diagonally arranged location relative to each other, of course, because of the relative orientation of the scissors' blades. A cutter element, typically an abrasive cylindrical rod, sits across the two openings where they meet. The actual sharpening involves placing the scissors through the plate with one blade in each opening. The operator then closes the scissors upon the sharpening rod and either pulls the scissors out or pushes it into the plate. In either event, the motion of the cutting surfaces of the scissors across the sharpening rod removes material from each of the blades to effectuate the sharpening. Placing the scissors on one side of the plate through the openings sharpens a right-handed scissors. Turning the plate around and entering the scissors through the other side accomplishes the same result for left-handed scissors. Sharpeners of this type appear in U.S. Pat. No. 1,051,333 to H. Jacoby and Des. 332,210 to O. Linden and are manufactured by Fiskars in Helsinki, Finland.
This sharpening device generally works well for most scissors. However, it loses substantial efficiency where the angle of the cylindrical bar across the two openings does not match the plane of the cutting edges of the two blades relative to their flat surfaces. This in effect can represent the result depending on the scissors' manufacturer.
Other types of sharpeners have seen regular use. Thus the leather strap found widespread use in barber shops for the honing of the straight-edge razor blade. The recent concern, however, over communicable diseases has caused barbers, even when they perform a shave, to use a disposable safety razor. The strap accordingly has lost favor since it does not serve to remove a substantial amount of the cutting edge of a knife that requires substantial sharpening.
Additionally, sharpening rods extending up to a foot or longer have found use in meat-carving sets. However, they often prove more difficult in use than sharpening stones. Furthermore, they require the operator generally to pull the knife of a blade held by one hand toward the other hand holding the sharpening rod. This of course creates the possibility of physical harm to the second hand.